A typical Liquid Crystal Display (LCD) cannot operate properly at low temperature due to liquid crystal (LC) characteristics. For an LCD to be visible, some type of heating system to warm and maintain a certain temperature is required.
Two approaches to heating and maintain proper LC temperature have been employed in existing LCD technologies. One is an external heater which is attached to the Thin Film Transistor/Indium Tin Oxide TFT/ITO cover glass following display fabrication. This approach provides maintenance heating by conducting current through the LCD cover glass. Because it occupies the inactive area surrounding the active LCD matrix and provides heat along the edges of the LCD and through the cover glass(es), an external heater is generally inefficient and unable to rapidly warm the display during cold start conditions.
Another approach is a row-line heater which is an internal heater integrated into the active matrix architecture of the display. The row line-heater can be used during cold start conditions to rapidly warm the liquid crystal material. The row-line heater is located within pixel array, very close to LC, so that it provides high efficiency, uniform heating inside of LCD glass.
FIG. 1 is an example of a row-line heater known in the prior art. This approach uses polysilicon row lines that also control the pixel transistors' input gates. Current can flow through the polysilicon row lines 10 to produce heat close to the pixel elements 20, and hence close to the LC material, but during the heating phase, no image can be shown with this approach, since the row transistors 30 and 32 are saturating the row lines 20 to heat them. CLC is the capacitance between the electrode 25 and an ITO common plate with the liquid crystal in between, and Cstg is the pixel storage capacitance. The warm-up time needed during cold start of the devices limits their usage in various applications of even this design.